Some fancy that the enigma is solved by the hypothesis of a diminished vital power ; but we have already attempted to show that the interpretation is without value, when applied to the cessation of development; the same reasons render it equally useless as a key to the hiero glyphics of decay. Not less vain were the endeavours of those who could satisfy their philosophy with such a subterfuge of ignorance as was afforded in the theory of a sum of exci tability, originally allotted to the system, and gradually exhausted, &c. ; as if excitability could possibly mean any thing more than an expression of the collective phenomena of ex citement, or vital movement. It is exactly on a par with the doctrine of decreasing vitality." ' Some talk prettily and poetically of the vital , flame burning out, of oil gradually wasting, of fuel expended,— phrases applicable enough as F metaphors, but absurd when propounded, as they too often are, as statements of matters t of fact.
When philosophy has failed to discover an- ; tecedences, she may still find a prolific source t of employment in the study of harmonies. f There is no event to be found in the relation of cause to those organic changes which, without the intervention of accidental agents, ultimately affix a bound to the duration of man's existence. - As no cause can be elicited for the termination of development, neither can we better explain why growth does not continue stationary, and maintain the bodily structures for a series of ages, so long as external circumstances remain the same. We live in the midst of agents that both supply us with life and infest us with poison : for a time we resist the baneful tendencies, and then gradually succumb, but in what manner we are at present ignorant. The prevalence of certain functions has been supposed to fortify certain animals against the outward agents or inward processes that would otherwise urge them to dissolution. The in fluence of respiration upon nutrition is well known, and consequently a large sum of respi ration has been alleged to account for the longevity of birds ; but there are equal or much greater instances to be found among fishes and reptiles, the amount of whose respiration is extremely small. In the one case the vitality is said to be less rapidly consumed, in the other to be more abundantly supplied ; expla nations which amount to little more than statements of the same facts in different lan guage. Lord Bacon was of opinion that birds owe their lengthened existence partly to the smallness of their bodies, and partly to their being so well defended by their teguments from the atmosphere ; while he accounted for the long life of fishes by the non-occurrence of desiccation in their aqueous element. There is nothing satisfactory to be obtained from speculations of this sort. The most that we can learn is the variation in the term of exist ence by the influence of various outward agents and modes of life. But whatever
variation may be discovered, it will still appear that climate, and time, and custom, and science have never prolonged the date beyond certain limits. The study of these circum stances, and the appliances of art, undoubtedly tend to enable a greater number to attain the extreme goal, but can never give the power of transgressing it. Vain, then, as Boerhaave observes, are the hopes of men who look for an Although at present, then, we cannot trace the causes of the bounded nature ofour existence, yet it is not difficult to discern its fitness to our constitution, and to the universal frame of things. The brevity of life is an ancient com plaint ; lamentations have been chaunted over it time out of mind : but its antiquity does not redeem this, any more than many other opinions equally hoary, from the character of a prejudice. Every consideration of the fact in question with reference to the universe must " justify the ways of God to man" in the dis position of this as of every other event. We have only to conceive the circumstance altered, in cor respondence to the idle wish of some aspirant to longevity, and we see that every thing else also would require to be changed ; that, in short, the beautiful arrangements of the world and of our social relations would be broken. To notice one or two of these : if the life of man were longer than it now is, his progeny would need to be greatly abridged from their present numbers, or they would soon exceed the ratio of subsistence. The time occupied in attaining maturity bears a direct proportion to the period of existence in the mammalia ; consequently, if life were prolonged beyond its present limits, that time during which the offspring of man is either helpless or very dependent on the parents, would be also length ened, and the accidents of disease or other casualties remaining the same, it is clear that confusion, distress, and manifold calamities would accrue to a rising generation. After the attainment of maturity and of its accompa nying faculties, it is not clear that any thing would be gained by the possession of these for a longer period than is now allowed; since we know but too well that men, after a time, lose the spirit of enterprise once engendered by the con sciousness of increasing or lately-acquireil powers, and fall into habits of action which they are unwilling to abandon, but which do not advance the resources of the species beyond a certain limit. Hence the advan tage of their giving way to others, to whom. they can commit their knowledge, and who, by their unworn energy, will advance it fur ther. " Life is sufficient for all its purposes if well employed," was well observed by Dr. Johnson ; and what follower of medicine can forget that the immortal sage of Cos, by the example which he afforded in his well-spent life, disarmed his own antithesis of its woful point : 6105 6o90c, n N Tixv4 !''axe".